Method and device for the prevention of selective corrosion of tubes and machinery parts of copper or copper containing alloys



F. VON WURSTEMBERGER. METHOD ANO DEVICE FOR THE PREVENTION OF SELECTIVECORROSION 0F TUBEIS AND MACHINERY PARTS OF COPPER 0R COPPER CONTAININGALLOYS.

Patented Mar. 30, 1920.

APPLICATION FILED JUNE II. I919.

UNITED STATES PATENT OFFICE. '1

FRANZ VON WURSTEMBERGER, 0F ZURICH, SWITZERLAND, ASSIGNOR TO AKTIEN-GESELLSCI-IAFT DER MASCHINENFABRIKEN ESCHER WYSS & CIE.. OF ZURICH,

SWITZERLAND.

METHOD AND DEVICE FOR THE PREVENTION OE SELECTIVE CORROSION OF TUBES ANDMACHINERY PARTS OF COPPER OR COPPER CONTAINING ALLOYS.

Application filed June 11, 1919.

To all whom it may concern:

lie it known that I, FRANZ voN WURsTEM- alumna, a citizen of theRepublic of Switzerland, residing at Hardturmstrasse 19,Zurich,Switzerland, have invented certain new and useful Improvements inMethods and Devices for the Prevention of Selective Corrosion of Tubesand Machinery Parts of (opper or Copper Containing Alloys; and I dohereby declare the'following to be a clear, full, and exact descriptionof the invention. such as will enable others skilled in the art to whichit appertains to make and use the same. reference being had to theaccompanying drawing, and to letters or figures of reference. markedthereon, which form a part of this specification.

For the prevention of selective corrosion of tubes and machinery partsof copper and copper containing alloys which are in contact with watercontaining ions, electrolysis may be employed to produce an easilysoluble hydrolytically decomposable acid reacting salt to neutralize thecorrosion qualities of the water.

The invention consists of a process to produce this preventive meansoutside of the main water stream in a separate vessel and furthercontrivances for the execution of this process.

Selective corrosion or pitting is understood to be the phenomenonwhereby fluids which according to their chemical composition are notconsidered as decomposers of metal heavily attack single areas ofmetallic parts which are immersed in the fluid or are in contact with itwhereas other parts remain unafl'ected.

This phenomenon occurs on anodes of copper immersed in sodium saltsolutions under the influence of electrolysis. oron aluminium anodes inchlorid solutions. In practice it is known as the cause of destructionof pump impellers and tube sets of copper and copper containing alloys.which are in contact with sea water or with water which conductselectricity. owing to the presence of any kind ofsalt wluch it containsin solution.

Specification of Letters Patent. Patented D1 30, 1920.

Serial No. 303,406.

Careful investigations have shown that the cause of selective corrosionis entirely due to the alteration of the surface of the metallic partsin question and not to the metal not being homogeneous, and that thephenomenon is due to electrolytically different qualities which thedifferent areas acquire under the influence of certain deposits. Assuch, slightly soluble salts of the metal in question come intoconsideration and accordingly selective corrosion does not occur inliquids which attack the metal but transform it into an easily solublesalt. The T0- duction of selective corrosion is due to the presence ofdifferent factors of a chemical and physical nature which are dependenton the nature of the metal in question as also on the salts contained inthe water.

One quality which water producing selective corrosion must possess atany rate is a certain electric conductivity. It does not follow howeverthat all water conducting electricity produces selective corrosion.

The behavior of copper and copper containing alloys in contact withwater which possesses a certain electric conductivity owing to thepresence of certain chemicals is briefly explained as follows:

Two different areas of a piece of metal immersed in the water are to beconsidered as two electrodes in short circuit. through the metal itself.At first as soon as the piece of metal is immersed a difference ofpotential usually arises between the two areas. which difference isdependent on the nature of the layer with which the surface of the twoareas are covered under the action of oxidation in the air beforeimmersion. The layer may only accidentally be absolutely the same onboth areas. Under the influences of this difference of potential onearea becomes an anode the other a cathode. However this difference ofpotential disappears quickly as the resulting electric current. producessalts on the anode, through which the concentration of metallic ionsthere is increased.

The galvanic element formed by the two areas is polarized in this way.By such local electrolysis the whole metal surface is brought in a shorttime to an equal potential which is higher than the potential of abright, newly immersed piece of the same metal.

A continuous attack on any spot is only possible where constant anodicdepolarization takes place. Such depolarization may occur throu hmechanical erosion of deposited anocIe products or through chemicaltransformation of those products into slightly soluble compounds, underchemical influence, which is equivalent to a reduction of theconcentration of metal ions on this spot. The polarizing layer which isfound on copper in water containing chlorid consists of protochlorid ofcopper CuCl and basic chlorids of various structure Cu (OI"I) Cl Asdepolarizers have been found: hot

water, which transforms CuCl by hydrolysis into protoxid of copper,further compounds of all sorts with alkaline reaction, which transformthe CuCl into Cu(OH), hydrate of protoxid.

The character of the attack due to such a depolarization depends on thenature of the deposit with alkaline reaction, for instance hydroxid ofmagnesium deposited in solid form will produce a distinctly limited areaof attack accordingto its slight solubility. On the contrary the easilysoluble caustic soda solution NaOH will act as depolarizer as far as itcan spread by diffusion.

As polarizers, i. e. chemicals favoring equalizing of potentials orpreventing local attack we have found an addition of acid to beessential. Direct addition of acid however is not practicable because ofits second ary action of destroying metals.

On the contrary, an addition of easily soluble hydrolyticallydecomposable salts of acid reaction as chlorid ofaluminium AlCl andprotochlorid of iron FeCl as well as chlorid of iron FeCl were found tobe good. In practice the best way to produce such a. salt is byemploying electrolysis.

According to the invention the electrolytic production of an easilysoluble hydrolytically decomposable acid reacting salt as preventivemeans takes place outside of the main stream of water in a separatevessel through which a branch of the water stream flows and carries withit the preventive means to the main water stream before it comes intocontact with the metal to be protected.

Contrivances according to the invention consist of electrodes throughwhich electric direct current flows and which are arranged in a vesselin such a manner as to keep the anode and cathode products separate fromeach other, the former of which serving as preventive means, the latterbeing carried away.

to circulate.

For this purpose the electrodes are placed in two chambers of a vessel,the chambers being separated from each other by a semipermeable wall andthrough which separate water streams are made to flow. The inlet of thechamber containing the electrode which is subjected to dissolution, isconnected to the main Water stream so that part of the corrosive waterflows through this chamber, takes up the preventive means produced thereand leads it into the main water stream.

In the chamber in which the cathode is placed, the cathode products areformed, such as hydrogen, caustic soda (NaQH) and other hydroXids. Theyare carried away by means of a special washing out device.

It is advantageous to use the vessel itself as cathode electrode.

If only a limited production of the preventive salt is desired theelectric current may be produced by the difierence of potential of twoelectrodes of different material, without employing an outer source ofelectricity. For instance a combination of an aluminium electrode with acarbon electrode immersed in sea water both connected togetherelectrically will produce a current which attacks the aluminiumelectrode and produces chlorid of aluminium AlCl Figure 1 shows anexemplification of the invention, I

Fig. 2 its application to a condensing plant. 1

Fig. 3 is a modification.

In the exemplification shown in Fig. 1-

the anode chamber is formed by a semipermeable clay well or diaphragmclosed at the top and at the bottom by covers 2 of insulating nonporousmaterial. A solid iron anode 3 is fastened to the upper cover. Throughthe pipe branch -.l which is connected to the delivery branch of thepump, salt water is admitted to the chamber; the water washes away theprotochlorid of iron FeCl which is formed at the anode and carries itthrough the pipe 5, which is connected with the suction branch of thepump, to the main stream of water, where on one hand it prevents theformation of basic chlorid of copper by forming basic chlorid of ironwith the air contained in the Water and on the other by itsownhydrolytic decomposition and of that of the FeCl it prevents thedecomposition of any chlorids of light metals present in the water. Theclay cell is surrounded by a cast iron casing 6 which acts as cathode.

In the space between cell and cast iron casing salt water supplied by apipe connected to the pump delivery pipe, is made The cathode roductsare discharged through the brane '7 into the discharge channel. 8 and 9are regulation devices on the circulating water piping.

water is tapped from the delivery branch 14.

of the pump 12 and through the pipe 16,

which is connected to the suction pipe of the pump, it is led back tothe main stream of water so that the electrolytic apparatus is in serieswith the main pump 12. A portion of the water is led through pipe 17,instead of pipe 15, to the cathode chamber in order to discharge thecathode products into the discharge channel 18.

Fig. 3 shows the contrivance containing electrodes ofdifi'erentmaterials. 19 is the vessel, 20 a carbon cathode, 21 an aluminium anode,22 is the semipermeable wall, 232& is the pipe line for the washing outwater of the cathode chamber, 25 26 are in and outlet branches for theWater flowing through the chamber of the anode.

The direction of the electric current is in-' dicated with arrows indotted lines.

An apparatus built in accordance with the invention can be installedanywhere near the plant for which it is required, Where the electricconnections, the water supply and discharge pipes or ducts can be easilyand satisfactorily arranged. As shown in the example the circulatingwater for the anode and cathode chambers can ,be taken from the mainpump or be supplied by an auxiliary pump.

No disadvantage is connected with the action of the anode products, andfurthermore the working of the device can be easily checked by examiningthe anode and its products.

In my copending application Serial No. 302,627, filed June 7, 1919,-Ihave shown another form of my invention.

\Vhat I claim now as my invention is:

1. The art of preventing selective corrosion. of water-contactingmachinery parts of copper or copper containing alloys, comprisingsupplying from a chamber separated from but connected to the water inletof such machinery a salt having, when hydrolyzed, an acid reaction.

2. The art of preventing selective corrosion of water-contactingmachinery parts of copper or copper containing alloys, comprisingforming in a vessel separate from but connected to the water supply ofsuch machinery a salt having an acid reaction when hydrolyzed.

3. The art of preventing selective corrosion of water-contactingmachinery parts of copper or copper containing alloys, comprisingforming by electrolysis in a vessel separate from but connected to thewater supply of such machinery a salt having, upon hydrolysis, an acidreaction.

1. The art of preventing selective corrosion of water-contactingmaclnnery parts of copper or copper containing alloys, comprisingforming by electrolysis between suitable electrodes in a'vessel a saltcapable of preventing such corrosion, said vessel being divided by anelectrolytic diaphragm into anode and cathode chambers, the anodechamber of said vessel being connected to the water supply forsaidmachinery to supply .anode products thereto, and the cathode chamberdischarging out of saidsupply.

5. The art of preventing selective corrosion of Water-contactingmachinery parts of copper or copper containing alloys, comprisingforming by electrolysis betweensuitable electrodes in a vessel a saltcapable of preventing such corrosion, said'vessel being divided by anelectrolytic diaphragm into anode and cathode chambers, the anodechamber of said vessel being connected'forv reception from and dischargeinto the water supply to said machinery, and the cathode chamberreceiving water from such supply and discharging to waste. I

6. The art of preventing selective corrosion of water-contactingmachinery parts of copper or copper containing alloys, comprisingforming by electrolysis between suitable electrodes in a vessel a saltcapable of preventing such corrosion, said vessel being divided by anelectrolytic diaphragm intoanode and cathode chambers one containedwithin the other, supplying water to and discharging anode solution fromthe interior anode chamber to the water supply for said machinery, andsupplying water to the cathode chamber and discharging cathode solutionto waste.

7, The art of preventing selective corrosion of water-contactingmachinery parts of copper or copper containing alloys, comprisingforming by electrolysis between suitable electrodes in a vessel a salthaving, upon hydrolysis, an acid reaction, said vessel being divided byan electrolytic diaphragm into anode and cathode chambers, the centralanode chamber being connected by a pipe to the discharge side of amachinery water supply pump and also connected by a pipe to the suctionside of such pump, and the outer cathode chamberconnected bya pipe tothe discharge side of such pump and the chamber arranged to dischargewater.

8. The art of preventing selective corrosion of water-contactingmachinery parts of copper or copper containing alloys, comprisingforming between dissimilar electrodes in water a salt having uponhydrolysis an acid reaction and capable of preventing such corrosion,supplying the anode solution to the machinery water and allowing thecathode solution to waste.

ing the anode solution to the machinery Water and discharging thecathode solution, said electrodes being contained in dia- 10 phragmseparated chambers.

In testimony that I claim the foregoing as my invention, I have signedmy name.

FRANZ VON WURSTEMBERGER.

